1. Field of the Invention
This invention relates to an optical tape recording and reproducing apparatus which records and reproduces information onto and from an optical tape by means of an optical head of the rotary scanning type.
2. Description of the Related Art
Various optical tape recording and reproducing apparatus which record and reproduce information onto and from an optical tape by means of an optical head of the scanning type are already known. An exemplary one of conventional optical tape recording and reproducing apparatus is shown in FIG. 7.
Referring to FIG. 7, the conventional optical tape recording and reproducing apparatus shown includes a laser light source section 101, a light beam separator 102, a light receiving section 103, a galvano mirror 104, a roof prism 105, a rotary drum 108 and an objective lens 109. A laser beam oscillated from the laser light source section 101 is converged by way of the light beam separator 102, galvano mirror 104, roof prism 105, rotary mirror 108 and objective lens 109 to an optical tape 110, which is wrapped on and being fed by the rotary drum 107. Reflected light from the optical tape 110 is returned by way of the objective lens 109, rotary mirror 108, roof prism 105, galvano mirror 104 and light beam separator 102 to the light receiving section 103. The components of the apparatus are thus controlled in response to information included in the reflected light received at the light receiving section 103 to record information onto the optical tape 110 or read out information recorded on the optical tape 110 by means of the laser beam.
When to record or reproduce information onto or from the optical tape 110, the laser light source section 101 is activated to emit a laser beam, which is supplied to the light beam separator 102.
The light beam separator 102 reflects, when a laser beam is supplied thereto from the laser light source section 101, the laser beam and supplies it to the galvano mirror 104. On the other hand, when a laser beam is supplied from the galvano mirror 104, the light beam separator 102 passes the laser beam therethrough and supplies the same to the light receiving section 103.
The light receiving section 103 includes a plurality of light receiving elements and receives, when a laser beam is supplied thereto from the light beam separator 102, the laser beam by means of the light receiving elements to produce a plurality of light reception signals, which are supplied to a controlling system or a reproducing system not shown of the optical tape recording and reproducing apparatus.
The galvano mirror 104 is controlled to change its angular position in response to a driving signal from the controlling system. At the angular position thus controlled, the galvano mirror 104 reflects a laser beam supplied thereto from the light beam separator 102 and supplies the same to the roof prism 105 or reflects a laser beam supplied thereto from the roof prism 105 and supplies the same to the light beam separator 102.
The roof prism 105 is driven to rotate by a rotator motor not shown to assure matching between a rotary optical system including the rotary mirror 108 and so forth and a stationary optical system including the galvano mirror 104 and so forth. When a laser beam is supplied from the galvano mirror 104 to the roof prism 105 while the roof prism 105 is being driven to rotate by the rotator motor, the roof prism 105 takes in the laser beam, and supplies it to the rotary mirror 108, but when a laser beam is supplied from the rotary mirror 108, the roof prism 105 takes in the laser beam and supplies it to the galvano mirror 104.
If the angular position of the galvano mirror 104 is changed during the operation, then a spot of laser light formed on the optical tape 110 is moved in a tracking direction in response to the change of the angular position.
The rotary drum 107 has a head face on which the optical tape 110 is to be wrapped and a drum motor for driving the head face to rotate at a speed equal to twice that of the roof prism 105. The drum motor operates in response to a driving signal supplied thereto from the controlling system to rotate the head face at the speed equal to twice that of the roof prism 105.
The rotary mirror 108 is disposed at a central portion of the rotary drum 107 and is rotated integrally with the rotary drum 107. When a laser beam is supplied from the roof prism 105 to the rotary mirror 108 while the rotary drum 107 is rotating together with the rotary drum 107, the rotary mirror 108 reflects the laser beam and supplies it to the objective lens 109, but on the contrary when a laser beam is supplied from the objective lens 109, the rotary mirror 108 reflects the laser beam and supplies it to the roof prism 107.
The objective lens 109 is disposed at a peripheral portion of the rotary drum 107 and is rotated integrally with the rotary drum 107. When a laser beam is supplied from the rotary mirror 107 to the objective lens 109 while the objective lens 109 is rotating together with the rotary drum 107, the object lens 109 takes in the laser beam and converges it upon the optical tape 110 which is wrapped on and is being fed by the rotary drum 107. The objective lens 109 takes in reflected light from the optical tape 110 then and supplies it to the rotary mirror 108.
With the optical tape recording and reproducing apparatus described above, however, a tracking error is obtained but only intermittently as different from an optical disk apparatus and so forth. Accordingly, in most cases, a tracking error signal at the point of time when feeding of the optical tape is started is sampled and a tape feeding motor is driven in response to a result of such sampling to finely adjust the feeding speed of the optical tape so that dynamic tracking movement by means of a tracking actuator is started from the center of a track and tracking movement is performed successively without track jumping.
According to the method, however, a track passing phase is controlled in response to a tracking error signal at a scanning starting position in place of a CTL signal, which is employed for CTL servoing in an ordinary magnetic video tape recorder apparatus, and dynamic tracking is additionally employed to effect tracking control in order to eliminate such a trouble as track jumping as described above.
With the method, however, since an optical tape, which is a resilient body, is moved and positioned by means of a motor having great inertia, the responsibility is low, and upon adjustment of the feeding speed, a sudden variation of the tension of the optical tape occurs and may damage the optical tape. Thus, it is a problem that it is difficult to effect stabilized servo feeding control.
A solution to the problem has been proposed wherein the feeding speed of an optical tape is fixed and a spot of a laser beam is kept at a next track entering position by means of a tracking actuator (for example, the galvano mirror 104 in the optical tape recording and reproducing apparatus shown in FIG. 7) which can be driven at a high speed at a region in which the optical tape is not wrapped on a rotary drum, and when the optical tape comes to the position, the tracking actuator is changed over to dynamic tracking.
With the solution, however, when the speed upon recording or reproduction is displaced a little or when some elongation or contraction of an optical tape occurs, a displacement of the track passing phase is accumulated so that the operating range of the actuator becomes very great. Consequently, an actuator must be employed which has the contradictory characteristics that it operates at a high speed and that it has a large range of movement. Accordingly, there is a problem that an actuator having such characteristics must be developed.